Books: Willing executioners: Hannibal by Thomas Harris Heinemann, pounds 16.99, 486pp

THERE ARE no surprises, no twists, no sustained threads of tension or terror in Hannibal - and there are not meant to be. This is not an unputdownable nerve-shredder, a simple machine designed to thrill and captivate. It is not Red Dragon Part Three, or even Silence of the Lambs Part Two. Its tone is often quasi-Biblical and ornately gothic. In place of forensic procedure, it features directly-addressed authorial thinkies: "Now that ceaseless exposure has calloused us to the lewd and the vulgar, it is instructive to see what still seems wicked to us." Its ending is repugnant, depressing and inconclusive. Hannibal is a morality tale, which just happens to feature a man who eats other people's brains.

Across the range of American popular fiction at the moment, many bestselling authors are doing what Harris seems to have done here. Having established the mass appeal and commercial infallibility of their branded products, they use the trust they have won from their readers and publishers as a platform from which to float a quite different type of book. Eating people's brains is disgusting - but then, small boys can do disgusting, with one finger and a nostril. To get away with "disgusted", you need a big talent, and a following to match.

Frightening fiction - whether it calls itself horror, crime or SF - is returning to its ethical roots. Once again it is learning to express rather than to invent its audience's nightmares. God is dead, or feckless. Established authority is worse than useless; democracy is wizened; capitalism has eaten itself.

Faced with "the incumbency of Mammon", decent, fearful Americans, who are neither red-necked nor effete, can only rely on good quality weapons, properly maintained and immaculately cleaned, wielded without rancour or cowardice by persons of honour.

"The world will not be this way within the reach of my arm," FBI agent Starling vows, before riding out to rescue Hannibal Lecter from one of his crippled victims. This meat magnate has only two remaining ambitions: to feed Hannibal to a herd of purpose-bred pigs, and to prevent the passage of the Humane Slaughter Act.

Harris is, as ever, a cunning unfolder; this time of character rather than of plot. (The plot here is slight; a revenge tragedy mixed with a thieves-fall-out black comedy). For most of the book, Red Dragon fans may fear that we are being shown so much of Hannibal's interior and hinterland that our suave demon, who prefers "when feasible" to eat only rude people, is in danger of becoming a cliche, a clown or a self-parody. Only in retrospect do we fully understand that Harris is systematically undoing the bulk of what he previously taught us about wickedness and dread.

The worst monsters, the man who invented the gentleman-psycho now tells us, are not self-aware, cultured cannibals but the empty-headed career- chasers, the shoulder-shrugging bystanders, petty and grand abusers of power, eye-for-an-eye revengers and - above all - those who, by making piecemeal accommodations with their consciences, gradually progress from cynicism to evil. When hunting monsters by torchlight, Harris warns us, beware the man who sold you the torch.

The deepest shivers here, along with the most startled laughs, come from Harris's unrivalled grasp of the details in which true horror hides. He sets extreme horror, which by its nature is beyond common experience, in the context of everyday awfulness and casual cruelty. For instance, in one of the many long asides in this gently paced book, Harris tells us more than we might wish to know about the vileness of modern pig farming. Indeed, Hannibal may well do for American pork what BSE did for British beef.

Red Dragon was one of the most extraordinary novels ever published. Readers coming to it for the first time, uncontaminated by sequels, cinema or reputation (if such readers exist) will always undergo an indescribably intense reading experience. Hannibal is a different matter altogether; not as phenomenal, certainly, but in its own way just as exciting. As a cultural event, even more than as a book, it is arguably the biggest shell yet fired in the battle to return mass fiction to the service of the masses.